I have a late 2013 15inch rMBP. Earlier today I tried to plug an hdmi cable into the hdmi from the port on my mac onto a TV. For some reason, it just wouldn't work; the TV screen just said "no signal" or something. My friend had to bring his laptop and he got his to work in an instant. He has a two year old HP. Sad that my super expensive mac can't do something this simple and his much more inexpensive computer has no issues. Any ideas?